Simultaneous quantitation of enalapril and enalaprilat in human plasma by 96-well solid-phase extraction and liquid chromatography/tandem mass spectrometry

A sensitive and rapid method based on liquid chromatography/tandem mass spectrometry (LC/MS/MS) combined with rapid solid-phase extraction (SPE) has been developed and validated for the quantitative determination of enalapril and its active metabolite enalaprilat in human plasma. After addition of internal standard to human plasma, samples were extracted by 96-well SPE cartridge. The extracts were analyzed by HPLC with the detection of the analyte in the multiple reaction monitoring (MRM) mode. This method for the simultaneous determination of enalapril and enalaprilat was accurate and reproducible, with respective limits of quantitation of 0.2 and 1.0 ng/mL in plasma. The standard calibration curves for both enalapril and enalaprilat were linear (r(2) = 0.9978 and 0.9998) over the concentration ranges 0.2-200 and 1.0-100 ng/mL in human plasma, respectively. The intra- and inter-day precision over the concentration range for enalapril and enalaprilat were lower than 13.3 and 15.4% (relative standard deviation, %RSD), and accuracy was between 89.2-105.0 and 91.9-104.7%, respectively.